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joob
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Kil
pipelines it's an enormous task the
platforms are interconnected and
interdependent so that adds to the
complexity what often surprises people
is that these platforms weren't designed
with decommissioning mind they were
designed at the height of energy crisis
to extract the oil and gas from the
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reservoir we have 154 Wells and that's
actually where the a lot of the effort
in decommissioning goes into plugging
and making safe those Wells so the
reservoir doesn't leak in the
future
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recy
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G
Technic
I really feel very strongly indeed that
having truly independent review is a
vital part of this
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process
gravity based structure or GBS as we
call it is made up of a steel skirt
which anchors the structure to the
bottom of the seabed it's made up of
some cells for storage and
legs these gravity based structures are
made of heavily reinforced concrete each
GBS weighs around 300,000 tons
sh when these GPS's were positioned out
offshore in the 1970s they would have
been towed out filled with ballast to
ensure that they were grounded on the
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sea
nobody's ever done this before you can
have a scenario pop up where you would
lose control of the GBS
structure is technically extremely high
risk of failure and also a very high
safety risk far higher higher than we
would accept in any other part of our
operations based on 30 years of data
gathered on North
operations that would indicate that we'd
have at least one fatality per gravity
based structure being
refloated that is a risk which I am not
prepared to uh to
entertain so having done some deep
technical studies and also dialogue with
our independent review group we we've
come to the conclusion that carry that
option
forward to better understand the
complexity around cutting concrete is we
have actually done some trials onshore
where we formed reinforced
concrete we've also compressed it to try
and replicate the conditions that are
out there actually on the gbss of
as she may appreciate making a cut
without trapping that wire with 6,000
tons of dead weight bearing down on that
cut surface in a marine environment
where you're dealing with the effects of
waves wind a dynamic situation is
certainly extremely
challenging
the UK taxpayer will be funding part of
the cost of of decommissioning so it's
really important that the operators are
looking to carry out the work in the
most cost- effective
manner
our recommendation based on 10 years of
study and uh independent review and
Analysis by our independent review group
is to leave the concrete gravity based
structures with the legs up in
place
one of our key contractors came to a
conclusion that actually the Collision
Hazard was about one in every 10,000
years so well under any accepted
standard
l
the option to leave the gravity based
structure in place really mirors what's
already happened in the Norwegian sector
where the structures have been left in
place uh with navigation Aids on there
to Aid shipping and fishing as a general
principle the fishing view is if it's
going to be there and going to cause an
obstruction then let's be able to see it
legs up is the choice of the
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fisherman
inside the gravity based structure there
are storage cells which have been used
to collect oil in and stored there until
it could be pumped away to a tanker or
via pipeline so this is a model of the
Brent Delta gravity based structure you
can see at the bottom There are 16
storage cells and this is a
cross-section through one of these 16
cells it's a reinforced concrete
structure the concrete is around 1 M
thick in
we drilled through the concrete at the
top of three of the cells and lowered a
series of liquid sampling and sediment
sampling tools all the way down so that
we could capture physical
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samples
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this is a sonar sphere which we
developed in conjunction with NASA and
what we were able to do with this is to
put it down through cell fill lines and
into the storage
cells and on the front we have a small
sonar which is what we used to
characterize the volume of sediment that
was in the base of one of the
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cells
for the samples for the sediment
certainly showed that the material was
more benign than we
thought
removing the contents of the cells is a
very demanding operation it would
require cutting a a hole into the uh the
cell itself so it can penetrating in
that nearly meter thick reinforced
concrete probably need to be quite a
large sizable hole to put dredging
equipment into the
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cells
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it's an enormous operation it's a
multi-season campaign we think this
isn't the right
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option we've heard Marine toxicologists
Marine
ecotoxicology uh underwater noise
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specialist while this had benefit it was
limited in its benefit because the cell
sediment could be 4 M thick but the
nutrients will only really affect the
top layer of that maybe 10 20
cm
as additional complexity associated with
the capping option was that the sediment
itself had a very low bearing capacity
and therefore any capping lay you put on
top would likely fall into the the
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sediment it sounds slightly
counterintuitive but on balance it makes
more sense to leave a sediment to
degrade naturally as it is in tuned
within the
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cells
there's quite a large volume of drill
curtains there our Specialists looked at
them they've considered the
environmental impacts and what was found
was that a Brent Alpha and Brent Delta
they were within osar limits Brent
Charlie they were fine at seabed but the
cell toop exceed one of the osar
criteria in terms of the oil load
released mobilizing the drill cuttings
is is like stirring up a muddy puddle if
you just leave the puddle as it is you
know he going to got clear water as soon
as you start to to mobilize it you then
got a more complex problem if you
disturbed then the disturbance itself
will create pollution and release the
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oil
the footings would require excavation
into the seabed to conduct an external
cut of those footings we would then have
to do the actual Cuts using some sort of
technique like Diamond Wire cutting or
High Press water abrasive cutting and
then you got the safety risk of of those
conducting the operation either through
uh remotely operated vehicles or through
divers to actually allow that cut to
take
place the outcome of that ca for the
jacket from environmental aspect is very
low impact if we leave those footings in
place fish system
we're prepared to live with that
provided the footings are well and truly
established in fish safe so that it is
entirely possible to know exactly what
is there and exactly where it
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is so there's 28 different pip lines in
the Brent field that we are looking out
for decommissioning these vary in size
from kind of 3 in up to over 30 in in
diameter some of them are more like
flexible hes in fact and some of them
are buried some of them are laid on the
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seabed smaller lines are relatively easy
to reverse reel so we would remove them
for the very big lines often they're
concrete coated to keep them on the
seabed they're
buried living with pipelines has been a
feature of our life for the last 50
years if a pipeline is trenched and
buried and has been for its life then
often the removal of it causes more
problems than leaving it
there
we are of course always open to new
views if there is anything that we've
not thought of uh then of course we are
more than willing to to listen and
learn
if we leave the structures in place of
course it doesn't stop there we have
liability on the structures forever we
will also be monitoring the structures
and the environment around them we
clearly want to do the right thing and I
spent many years studying the issue to
understand what that right thing is what
we've come to is a very robust and
really indepth decommissioning proposal
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f